This invention relates to printing presses and more particularly to apparatus for threading a web through a printing press.
A rotogravure printing press, for example, may include ten units, each of which has an impression roller and a design cylinder for applying ink to the web and numerous other rollers for conducting the web through a dryer, compensator and other press sections. Accordingly, it is time consuming to thread or pull a web from the unwind roll to the folder slitters, and prior art webbing systems often result in web wrinkles and breaks.
Conventional webbing systems use chains, or a pair of spaced cables or chains with a bar or elastic band suspended therebetween across the press, if the press is not webbed by hand. Some systems have independent drives, some require the press to be driven during webbing, and some require both.
The link and sprocket arrangement of a chain drive results in a chain path that can only approximate the web path, creating slack and/or tight webs that cause wrinkling of the web and web breaks during webbing. Other difficulties with a chain drive are that unacceptably high chain tensions result and that the chain usually does not stay on the sprockets.
Webbing systems using a bar across the press require press elements such as register eyes, drop rollers, etc. to be moved out of position to permit passage of the bar. Some systems require the press to be operating in order to pull the web through the press, creating the problem of matching the speeds of the webbing system and the press.
These and other disadvantages of the prior art webbing systems are overcome by the present invention.